Windows and doorways having arched headers have long been popular architectural additions to homes and buildings. Such windows and doorways typically include a wooden jamb that has spaced vertical members joined at their top ends by a curved or arched wooden header. Although the vertical members of such casings are easily fabricated, reliable methods of fabricating high quality arched wooden headers have long evaded woodworking craftsmen. In one method of crafting such headers, elongated wooden blocks are mitered at their ends and secured together end to end to form the general shape of the arch. The curve is then cut with a band saw to form the arched header, which can then be machined if desired and secured to upper ends of the vertical jamb members. Headers fabricated in this traditional way have had several shortcomings. The butt joints between the blocks, for example, tend to separate over time due to changes of temperature and moisture-induced expansion and contraction of the adjacent blocks. Further, such headers generally are not suitable for staining because the skewed relative orientations of the wood grain of adjacent blocks usually is not considered visually attractive. Consequently these headers often are limited to use in door and window frames that are to be painted.
In a more recent method of fabricating arched headers, a plurality of thin wooden boards are stacked with glue applied between adjacent boards to define a laminate. The stacked boards are placed atop a convex form and an elongated metal band is positioned to extend along the top board and overlie the stack. The ends of the band are then drawn toward the ends of the convex form such that the boards are bent by the band toward engagement with the form. The forces applied by the band to the stacked boards are maintained until the adhesive has cured. This method has certain drawbacks. Bending wood strips into an arcuate form with pressure applied downwardly on each end results in having upward pressure applied to the center portion of the strips and little or no pressure applied intermediate the center portion and the ends. As a result, the individual strips are prone to cracking and are subject to a significant amount of surface friction and sliding motion between layers that interferes with proper compression. In addition, the relatively thick adhesive tends to become trapped between individual lamina in excessive amounts due to surface imperfections in the lamina, ripples formed in the laminae during bending or the uneven application of pressure. As a result, the product quality is uneven and the method is unreliable.
Another known method of forming arcuate pieces is a mass production operation in which hydraulic presses are used to form the arches. In this method, arcuate rams are forced into concave forms with the wood lamina trapped and compressed therebetween. This method is capable of producing large quantities of headers, for example, but is unsuitable for custom work in individual structures and necessitates the use of thin highly flexible lamina which detracts from the finished appearance and adds to the cost. Many of the problems inherent in prior art methods using steel bands are also present with the hydraulic press method.
Thus, a need exists in the art for an apparatus and method of forming arcuate structural members that avoids the disadvantages of the prior art while producing pieces of a quality superior to that of pieces produced by prior art methods. It is to the provision of such an apparatus and method that the present invention is primarily directed.